Method and apparatus for blood withdrawal and infusion using a pressure controller

Abstract

A method and apparatus for controlling blood withdrawal and infusion flow rate with the use of a pressure controller. The pressure controller uses pressure targets based upon occlusion limits that are calculated as a function of flow. The controller has the ability to switch from controlling withdrawal pressure to controlling infusion pressure based upon the detection of an occlusion. The controller distinguishes between partial and total occlusions of the withdrawal vein providing blood access. Depending on the nature of occlusion, the controller limits or temporarily reverses blood flow and, thus, prevents withdrawal vessel collapse or reverses blood flow to quickly infuse blood into the vessel without participation from operator.

1. A method of controlling an extracorporeal blood circuit comprising the steps of:
 a. withdrawing blood from a withdrawal blood vessel in a patient into the extracorporeal circuit; 
 b. determining a withdrawal blood pressure in the extracorporeal circuit; 
 c. withdrawing blood at a flow rate selected to reduce a difference between the withdrawal pressure and an occlusion limit which is a function of blood flow through the circuit and withdrawal pressure; and 
 d. temporarily reversing blood flow to infuse blood from the circuit into the withdrawal blood vessel if the flow rate selected in step (b) is reduced to below a predetermined limit. 
 
     
     
       2. A method of controlling an extracorporeal blood circuit as in  claim 1  wherein the predetermined limit is a blood flow rate of substantially zero. 
     
     
       3. A method of controlling an extracorporeal blood circuit as in  claim 1  further comprising the steps of:
 e. detecting an occlusion which at least partially blocks the withdrawal of blood from the patient, and 
 f. temporarily reversing a flow of the blood to infuse blood from the circuit into the withdrawal blood vessel if the step (b) of the algorithm is unsuccessful in maintaining significant blood flow. 
 
     
     
       4. A system for controlling blood flow withdrawn from a patient comprising:
 an extracorporeal circuit having a blood passage including a blood withdrawal tube, a treatment device and an infusion tube; 
 a pressure sensor coupled to said withdrawal tube and sensing a blood pressure in the withdrawal tube; 
 a pump coupled to the circuit and adapted to move blood through the blood passage at a controlled flow rate, and 
 a pump controller receiving a blood pressure signal from the pressure sensor and controlling the pump to automatically adjust the controlled flow rate, wherein the pump controller includes a processor and a memory storing a control algorithm for a variable withdrawal pressure target as a function of the controlled flow rate, said controller reduces the controlled flow rate based on a difference between a withdrawal pressure sensed by the pressure sensor and the withdrawal pressure target, and said controller reverses blood flow to infuse blood into the patient through the withdrawal tube if the controlled flow rate is reduced below a predetermined limit. 
 
     
     
       5. A system as in  claim 4  wherein the pump controller includes a proportional integral feed forward pressure controller. 
     
     
       6. A system as in  claim 4  wherein the treatment device is a hemofilter. 
     
     
       7. A system as in  claim 4  wherein the treatment device is a dialysis device. 
     
     
       8. A system as in  claim 4  wherein the pressure sensor is a real time sensor providing real time pressure signals to the pump controller. 
     
     
       9. A system as in  claim 4  wherein the pump includes a direct DC drive motor. 
     
     
       10. A system as in  claim 9  wherein the drive motor is a brushless motor. 
     
     
       11. A system as in  claim 4  wherein the treatment device is a blood filter. 
     
     
       12. A system as in  claim 4  wherein the pressure controller alternatively controls a withdrawal pressure and an infusion pressure by synchronized switching.